Textile braids are fibrous architectures obtained by interlacing of threads (threads, roving, ribbons or bundles of threads). Thread arrangements relative to each other are defined by the shape and characteristics of the object to be obtained. The simplest braid that can be made, also called a mat, is composed of only three threads, in which one of the two external threads is alternately placed in the centre by crossing over, so that each thread periodically passes into the centre from one side and then from the other side of the braid. Braids composed of a larger number of threads are made using the same interlacing principle but more generally, with threads that follow the same direction over a longer distance.
“2-D” braids are composed of biaxial and triaxial braids. Biaxial braids are composed of two groups of threads that cross over each other at an angle of ±θ, where θ is defined as the braiding angle. FIG. 1 diagrammatically shows a biaxial braid composed of a first group of threads 1 and a second group of threads 2 that cross each other. The braiding angle θ can vary between about 5° and 85° between a braiding axis x and an axis of inclination y, these values being practical manufacturing limits.
The triaxial braids are composed of the presence of an additional group of threads in line along the braiding direction (θ=0°). FIG. 2 shows a view of a triaxial braid composed of a first group of threads 3, a second group of threads 4 and a third group of threads 5 aligned along the braiding direction. Interlacing patterns are defined by two numbers: the number of threads above which a thread in the opposite group passes followed by the number of threads below which it passes. The main patterns used are (1, 1) (diamond braiding), (2, 2) (normal braiding), (3, 3) (Hercules braiding). The braiding thickness is constant and is equal to the thickness of 2 threads (biaxial). If a part is to be completely covered when covering a form (that may or may not be eliminated later), the ratio of the diameters must remain between 1 and 3, corresponding to an angle that can vary between 20° and 70°. Nevertheless, note that the mechanical strength is not the same in zones with different diameters and it also varies by a factor of 1 to 3. The tubular braids are obtained by doing the braiding either directly on a liner (or envelope) from which the part to be obtained is made or on a mandrel. Thick structures are made by stacking several layers of braids together (patterns may be different) on each other.
“3-D” braids are an extension of “2D” braids obtained with simultaneous braiding of several layers of “2D” braids with a periodic connection from layer to layer. This type of texture is also known as “interlock braid”. This can give greater thicknesses, connections between layers (leading to better mechanical properties such as a better resistance to delamination) and more complex and more precise forms.
Braiding is a very old traditional textile technique (1748, weaving loom made by Thomas Wadford), originally used to make ropes, laces and reinforcement for tubes.
FIG. 3 shows the principle diagram of a circular braiding machine like that described in the “Handbook of Composite Reinforcements” by Y. Ed. Lee et al.
A 2D braiding machine that can be either vertical or horizontal is composed of a set of spindles 11 (thread bobbin supports) that move inside a guide path defined on a table and according to a braiding plane 12. For a simple circular braiding machine for making tubes, the spindles follow undulating paths around the periphery of the circular table, half in one direction around the circle and the other half in the other direction, the two paths being interlaced as shown in FIG. 4. A straight displacement system 14 perpendicular to the braiding table is synchronised relative to the movement of the spindles to hold the braid 13, possibly on a mandrel 15. Information on this subject can be found in article N 2511 in Techniques de l'Ingénieur (Apr. 10, 2006) and the “Handbook of Composite Reinforcements” mentioned above. Reference 16 represents the convergence zone of threads to be braided 17. Reference 18 represents an axial thread, and reference 19 represents an axial thread-guide.
The ratio of the spindle displacement speed to the mandrel displacement speed defines the braiding angle. The ratio of the number of bobbins relative to the number of intersections defines the type of the braiding pattern made. The addition of fixed bobbins can give triaxial braids. If the spindles turn back after some distance instead of making complete turns, then flat braids are obtained. Spindles comprise uniform tension systems, for tensioning or for compensating of threads (the distance from a spindle to the convergence zone on the braid not being constant) to obtain braids with uniform patterns and required compactness. As mentioned above, the thickness of a layer (biaxial braid) is equal to twice the thickness of a thread. Conventionally, a thick tubular part can be obtained by stopping displacement of the mandrel when the required length has been braided, the threads can be cut and a second pass can be made, and then the operation can be repeated until the required thickness is obtained.
There are two types of 3D braiding machines. The first is said to be rectangular, with an alternating movement along two directions in order to obtain “Cartesian” braids. The second type is circular with an alternating movement in the radial and circular directions, resulting in “polar” braids. Sections with different shaped cross-sections can be obtained by predetermined positioning of the spindles on the machine in the initial state. Hollow sections are obtained by polar braiding, solid sections are obtained by Cartesian braiding. Further information on this subject can be found in article N 2511 in Techniques de l'Ingénieur, mentioned above and in “Handbook of Composites” by G. Lubin et al., Springer, 1998.
Structural composite materials are composed of fibrous reinforcement such as braids and a matrix that is the material between the fibres (and gives cohesion to the material). They are characterised by different types of matrices:                organic matrices: thermoplastic or thermosetting,        metallic matrices,        mineral or ceramic matrices (glass, carbon, silicon carbide, etc.).        
There are no braided tubular structures closed at one or both ends. Due to the inherent principle of 2D and 3D braiding (see FIG. 3), the braids cannot be closed because the start and the end of the operation begin and end with parallel threads (in bundle), either held together at the formation point (start of braiding) or ending up at the bobbins (end of braiding). Braiding begins and ends on diameters between two values dependent on the braiding angles. No technical literature and no patents describe any way of making structures for which the main body is a braid and that are capable of continuously obtaining forms with a smaller diameter than the minimum diameter or for closing it, for all threads. Further information about this subject can be found in the article “A Comparison of Helical Filament Winding and 2D Braiding of Fiber Reinforced Polymeric Components” by M. Munro et al., Material and Manufacturing Processes, vol. 10, No. 1, pages 37 to 46, 1995. Existing solutions to close braid-based structures, particularly necessary for pressure vessel applications, include metallic inserts at the ends.
U.S. Pat. No. 7,204,903 very briefly discloses an innovative solution. Braiding is done on a liner that is cylindrical shaped at the centre and hemispherical (domes) at the ends. At least one of the domes has an insert at its end (pole). Braiding is conventionally done on the cylindrical part and on the hemispherical part as far as the insert. The innovation lies in the fact that at this moment, a second layer is made by stopping braiding and turning the bobbins (by about 180°), instead of starting in the opposite direction; half of the bobbins turn in one direction and the other half turn in the other direction which puts the bobbins opposite their initial position. Braiding is then resumed (next layer) along the inverse direction to the previous direction. The advantage mentioned compared with conventional braiding is that there is no need to cut the threads or to bend them and fold them over if they are sufficiently flexible, when changing from one braiding layer to the next. The result of the fabrication method used is that during the 180° rotation, one layer out of two in the hemispherical part corresponds to thread placements without any connection between each other (equivalent to filament winding) and a large thickness at the insert (the threads overlap each other in contact with the insert). Note that no value or information is given about braiding itself or the diameters of the cylinder or the insert, neither in the description of the invention nor the examples (the only numerical value is the rotation angle between two braids). The information in this patent does not solve the problem of closing one end, simply the integration of an insert. Furthermore, the invention does not offer a solution for the small diameters problem.
Document US 2008/0264551 discloses the fabrication of composite vessels (cylinder and hemispherical bottoms) based on dry threads (not impregnated with resin) for the storage of low or high pressure gas. The invention lies in the fact that the internal liner acts as a mould during injection of the resin and also as a heating or cooling system during polymerisation. Braiding is done by a combination of biaxial or triaxial braiding on the faces of the domes, by turning over and deforming the biaxial braid and sealing the ends of the threads by a means such as gluing. According to the authors, this method gives good control over the thickness and the contour. This system uses conventional braids and it does not result in continuity of the threads on the domes because their ends are glued, nor closing based on threads.
Document WO-A-89/05724 discloses the fabrication of a bottle made of a composite material at a moderate price for the storage of high pressure gas. The ends of the bottles comprise two end pieces connected to each other through a central rod, one of the two being used for adding or drawing off of gas. The body of the bottle is composed of coaxial braids with a resin matrix. The ends may be truncated or hemispherical, made of metal or plastic. This document does not describe the braiding technique, apparently the braids used are standard. Nor does this patent describe how to make closed braids because the ends are composed of inserts at the ends.
Document EP-A-0 487 374 presents a high pressure gas storage vessel composed of threads placed by filament winding and/or a braid. The vessel is cylindrical in shape with bottoms. It gives no information about the braid used other than that it is used as a longitudinal reinforcement and therefore a priori on the cylindrical part. There is no description of a closure by a continuous thread.
U.S. Pat. No. 3,765,557 presents a means of making a high pressure vessel made by filament winding in which the standard thread is replaced by a braided thread. Therefore, this patent does not apply to the braiding technique and gives very different structures. It is also conventional to be able to obtain a closed end, but with an overthickness by filament winding.
U.S. Pat. No. 5,070,914 discloses a new woven architecture and its fabrication means. The technique is based on weaving, with threads starting radially and circumferentially woven threads following a spiral. These structures are based on a path of threads following the line of a spiral without any cylindrical or axial symmetry, unlike the invention which will be described in appended claims.